Piezoresistive based sensors, or sense die, may be used to measure the pressure in many applications, including manifold absolute pressure (MAP) applications, exhaust gas recirculation (EGR) systems, low pressure fuel measurement applications, and the like. Typically, in these applications, fluid interacts and measurements are taken from the side of the sense die having pressure-sensing circuitry and wire connections. FIG. 11 illustrates an example of a sense die 100 implemented in the prior art. As depicted, resistors 101 are implanted in a piezoresistive silicon substrate 102. Metal contacts 104 are also implanted in the substrate 102 and separately connected to each end of the resistors 101. A diaphragm 106 is disposed over the substrate 102 and resistors 101. When a fluid or other medium invokes a force in the direction 108 illustrated, the diaphragm 106 flexes, which alters the crystal structure of the substrate 102 and is detected by resistors 101. Wires 110 connected to metal contacts 104 transmit signals corresponding to the detected force.
In order to protect the sense die 100 from degrading effects of fluids, a gel (not shown) is applied to cover the surface of the sense die 100 and wiring 110, metal contacts 104, diaphragm 106, etc. The wires 110 and metal contacts 104 typically include an increased amount of gold or the gold is replaced entirely with platinum. These measures protect the sense die 100, wires 110, and contacts 104 from degradation over time. However, problems become apparent when the pressure medium contains corrosive elements. The corrosive elements tend to infiltrate into the gel, aggressively corroding the wiring, bonds, metal contacts 104, and the sensing die 100.
Conventional techniques for securing the sense die 100 to a medium require a detailed process of forming a glass on the underside of the substrate 102. The glass attachment technique firmly secures the sense die 100, and the integrity of the attachment remains consistent over a wide pressure range. However, the glass attachment to the silicon sensing element unnecessarily increases cost and manufacturing time due to the complexity, which is undesired in pressure-sensing applications that do not operate in the full operating range of a glass attachment. Accordingly, a need exists for a less complex and less costly attachment technique, while protecting the circuitry associated with the sensing die from the pressure medium as well as outside environments.